Method of making wires scribed circuit boards

ABSTRACT

This invention relates to interconnection circuit boards and processes for making and modifying interconnection circuit boards wherein adhesive is applied to a wire used in scribing a conductor pattern. The adhesive is activated to a tacky state during the wire scribing operation which forms the conductor pattern, and can thereafter be cured to permanently bond the conductors to the board surface.

RELATED APPLICATIONS

The following applications filed concurrently herewith contain relatedsubject matter and are incorporated herein by reference: (1) "Method ofManufacturing Interconnection Circuit Boards" by Ronald Morino, BrianEdward Swiggett, Raymond J. Keogh and Jonathan Clark Crowell; U.S. Ser.No. 06-756,691 (2) "Heat Activatable Adhesive for Wire Scribed Circuits"by Andrew Jed Schoenberg and Marju Laube Friedrich; U.S. Pat. No.4,642,321, issued Feb. 10, 1987 (3) "Apparatus for Making ScribedCircuit Boards and Circuit Board Modifications" by Brian EdwardSwiggett, Ronald Morino, Raymond J. Keogh and Jonathan Clark CrowellU.S. Ser. No. 06/756,690.

BACKGROUND OF THE INVENTION

This invention concerns scribed interconnections and processes forproducing same. More particularly, this invention concerns discrete wireinterconnections and processes for scribing conductors on a surface of asubstrate to form or to modify point-to-point electrical connections.

Processes that employ wires as the interconnection medium in theproduction of circuit boards are known. In one such process, known asthe Stitch Weld™ process, a standardized circuit board panel isutilized. The panel is comprised of pads and circuit holes representingvarious component sizes and pin densities of components. Components tobe used in the circuit are matched to fit existing pads and holes on thestandardized panel. Interconnection is achieved by welding endpoints ofeach wire to pads on the panel. This allows wires to be looped acrossthe board between endpoints. Component insertion in this process isdifficult. Wires typically cover the entire board thereby blocking areaswhere components are to be placed. Automatic component insertion, inmost cases, cannot be used because component leads would get tangled inthe wires.

U.S. Pat. No. 4,414,741 to Holt attempts to alleviate the "looping"problem of the Stitch Weld™ process. Holt describes placing temporarypins on a circuit board panel to define channels which do not interferewith component locations. Wires are routed within these channels andwire endpoints are soldered to the appropriate pads. The temporary pinsare removed and the circuit board is covered by a plastic sheet whichencapsulates the wires to retain them in the channels. However, thisprocess has a number of disadvantages. First, wires still loop acrossthe surface of the board from ends of the channels to wire terminationpoints. Second, because certain portions of the circuit board arededicated to the channels, the potential component density of the boardis greatly diminished. Third, special holes must be drilled in thecircuit board substrate to accommodate the temporary pins. Lastly,electrical interference and signal distortion may arise because amultiplicity of wires are positioned closely together in the channels.

Floury, et. al., "An automatic wiring eguipment for hybrid substrates",Proceedings of the 32nd Electronic Components Conference, May, 1982,describe another process for construction of circuit boards, wherein afine line of adhesive is first dispensed along the desired wire paths.Wires are subseguently routed over the adhesive to bond wires to thecircuit board. Endpoints of the wires are then bonded to pads. Thisprocess is inefficient, as it reguires the additional step of routingall wire paths with adhesive before placement of the wires on a board.The step of placing adhesive on the board prior to wire placementdoubles the manufacturing time of the process. In addition, when wirescross over one another, there is no adhesion between the wires.

U.S. Pat. Nos. 3,674,914, to Burr; 3,674,602, to Keogh and Canadian Pat.No. 1,102,924 granted June 9, 1981, all incorporated herein byreference, describe a process and apparatus wherein wire is scribed ontoan insulating base. A strand of preformed wire is fed continuously ontoa surface of the base. The wire is simultaneously affixed to the basesurface and cut at a predetermined terminal point on the base therebyproducing a predetermined interconnection pattern. In practice, and asdescribed in the patent, the wires are adhered to the surface of thebase by applying adhesive to the base surface and activating theadhesive when the wires are scribed to the surface of the base. Adifficulty of this arrangement, however, is that when activated on theboard, the soft adhesive may allow the wire to drift or swim before thewire becomes adhesively set. This may lead to short or open circuitswhen the wires are not in their desired positions on the board. Thesepatents also suggest the possibility of applying adhesive to the wiresprior to the scribing of the wire conductors. However, there is noteaching of how to practice this suggestion.

European patent application No. 113,820 published July 25, 1984,describes a process wherein wire is scribed on a photocurable layer onthe surface of a circuit board. The photocurable coating which receivesthe wire is softened prior to or at the time of scribing and issubsequently photocured. In the preferred form, ultrasonic energy isused to soften the adhesive layer and light energy is used to cure thephotocurable adhesive layer.

U.S. Pat. No. 4,450,623 to Burr describes a process wherein wires arescribed on an adhesive-coated surface of a substrate having etchedconductive pads representing terminal and inflection points in thecircuit. Where the wire contacts a pad, it is soldered or weldedthereto. Heat and pressure is then applied to the board to activate theadhesive and to embed the wire conductors into the substrate surface.Burr mentions the possible use of wire coated with adhesive. As before,once the wire has been scribed and soldered, heat and pressure isapplied.

Japanese Laid Open application No. 57-136,391, published Aug. 23, 1982,describes a process wherein wires are scribed in a predetermined patternonto an adhesive-coated surface of a substrate. Laser energy is used tosoften the adhesive prior to scribing the wires.

British Patent Specification No. 1,504,252, published Mar. 15, 1978describes a method of bonding and soldering insulated wires in apredetermined pattern on an insulating base support to establishelectric contacts between conductive zones on the base support. Adhesiveused for bonding the wires is deposited on the surface of the basesupport as a film layer in which heated wires may be embedded.Alternatively, a dry film coated wire is suggested which can be madeself adhesive by heating or passing through a suitable solvent.

Wired circuit patterns have been made using a heated roller to embedenamel coated wire into an adhesive-clad substrate. The endpoints of thewire are soldered to exposed solder-coated pads on the substrate'ssurface. The adhesive is carefully applied to the sustrate by silkscreen prior to the embedding step so as not to contaminate the solderpads and holes.

In another process, pre-perforated adhesive sheets are placed on thesurface of a substrate having surface pads and holes. The perforationsexpose predetermined areas in which holes and surface feature will beplaced. Conductors are then placed on the adhesive surface. However,each different board reguires its own special perforation pattern,making it cumbersome to use.

Processes that employ wires as the interconnection medium in themodification of printed circuit, multilayer and wire-scribed circuitboards are also known. These modifications may be reguired for differentreasons. A circuit interconnection sequence may have to be changed bythe designer to accommodate newly designed functionality on the circuitboard. A conductor may be omitted or a misconnection may be made duringthe design process. A circuit board modification also may be required tocorrect a defect on the board that occurred during manufacture.

Repairing or modifying circuit boards is more economical and efficientthan redesigning or manufacturing replacement circuit boards. The boardsare typically modified by cutting unneeded connections and using smallinsulated wires commonly called "jumper wires". This wire additionprocess requires manual soldering of the wire endpoints. In thisprocess, wires are usually looped away from the board. As greaternumbers of jumper wires are added to the board, the circuit boardbecomes an unwieldy mass of looped jumper wires, commonly called a"rat's nest". The "rat's nest" often impedes or prevents the use ofautomatic component insertion, automatic soldering equipment andautomatic circuit board test equipment, thus requiring additional manualoperations which are time-consuming, error prone, and costly.

This manual jumper wire approach is economical only in low volume, lowcircuit density applications, where only a few additions are necessary.When high volume circuit board producers are forced to use this process,it is extremely costly because it is labor-intensive. Additionally, thisprocess does not result in repeatable precise geometrical wire placementon all boards in a manufacturing lot. Also, defined impedance isdifficult to achieve with jumper wires and reproducible electricalcharacteristics may be difficult to maintain.

Developments in semiconductor technology have increased thefunctionality of semi-conductors, i.e., the number of operationsperformed by the semiconductor, while decreasing the size of the overallsemiconductor package. This results in a greater number of contactpoints in a smaller area for interconnection. Because of the greaternumber of contact points, the circuit board must provide for a higherdensity of interconnect per unit area.

This increases the probability of committing errors during a manualmodification process. The close proximity of contact points or circuitterminal points on high density boards increases the probability ofunintentionally modifying an erroneous endpoint.

Webizky et. al., "Making 100,000 Circuits Fit Where At Most 6,000 FitBefore", [Electronics Vol. 52, No. 15, (8-2-79)] describe a processwherein one surface of a circuit board is dedicated to patternmodifications. Although this process may improve the circuit boardrepair time, an additional circuit layer must be added to the board toaccommodate the changes. This increases the manufacturing time and costas well as the size of the circuit board package.

Processes for automatically repairing/modifying have been proposed.These include automatic positioning devices, optical light spotindicators, and laser soldering eguipment. These processes have helpedto increase productivity, but they are still heavily dependent on manualplacement of conductors or jumper wires. All the automated processesrequire a smooth, flat surface for modification.

U.S. Pat. No. 4,327,124 to DesMarais describes a process for screenprinting circuit modifications on an etched printed circuit boardwherein a dry photoprintable film resist is laminated on the circuitboard over the existing conductors, exposed, developed, and cured. Toapply the modifying conductors, a metal loaded, conductive polymer inkis applied through a screen to the film resist layer in the pattern ofthe conductor modifications. The circuit pattern is then covered with aconductive metal powder while the conductive polymer ink is still wet.The powder is pressed into the ink and the composition is cured. Afterthe curing step, solder is screen-printed over the copper ink. Thesolder and copper are then fused together in an infrared reflowsoldering machine. This process has many disadvantages and has not beenwidely adopted.

OBJECTS OF THE INVENTION

It is, therefore, an object of this invention to provide a process forefficiently and accurately manufacturing interconnection circuit boardsand the circuit boards produced thereby.

Another object of the invention is to provide a process for constructingwire scribed circuit boards which does not require surface preparation,including application of an adhesive layer, prior to placement ofconductors.

Still another object of this invention is to provide a process forinterconnection in which the conductors can adhere to various types ofsurfaces and surface topographies.

Another object is to provide a process and apparatus for repairing ormodifying circuit boards such that the repaired or modified circuitboards can be subsequently operated on by automatic component insertion,automatic soldering and automatic testing equipment.

An object of this invention to provide an automated process andapparatus to repair or modify circuit boards that can be employed at anystage of manufacture.

An object of this invention is to provide a process and apparatus forrepairing interconnection circuit boards after components have beenplaced on the circuit board.

An object of this invention is to provide an automated process andapparatus for repairing or modifying interconnection circuit boards withrepeatable precise geometric placement of conductors on boards.

Other objects and advantages of the process and apparatus will becomeapparent throughout the discussion hereinbelow.

DEFINITIONS

The following terms used throughout this specification have the meaningsdefined below:

A "conductor" is at least one preformed, elongated filament having atleast one portion, a "conductive portion", capable of conducting energy,such as electrical energy or light energy. Conductors may be coated withan insulation layer.

A "substrate" is a base having a surface on which a circuit pattern maybe produced. A substrate may already have a circuit pattern on itssurface.

"Wire or conductor scribing" is a process by which conductors areapplied and affixed to a substrate in a predetermined pattern to form acircuit pattern.

"Tacky" is the property of an adhesive which enables it to form a bondof measurable strength immediately after it is brought into contact witha substrate.

"Blocking" is undesired adhesion between touching layers of a materialsuch as occurs under moderate pressure during storage or use.

An "interconnection" is a process or system permitting the joining ofdiscrete conductor connections.

"C-stage" is the final stage in the reaction of certain thermosettingresins in which the material is relatively insoluble and infusible.

A "thermoset" material is a material that will undergo or has undergonea chemical reaction by the action of heat, ultrasonic energy,ultraviolet light, etc. leading to a relatively infusible state.

A "conductor endpoint" is the point of a conductor which can be attachedto a terminal point.

A "heat activatable" adhesive is a dry adhesive film that is renderedtacky or fluid by application of heat or heat and pressure.

A "light activatable" adhesive is a dry adhesive film that is renderedtacky or fluid by application of light energy.

A "hot melt adhesive" is an adhesive which is applied in a molten stateand forms a bond upon cooling to a solid state.

A "terminal point" is at least one point at which an interconnection ismade with a conductor. Terminal points can be surface pads, holes orapertures with or without metallized walls, conductive cavities,conductive leads, conductive fingers or the like.

SUMMARY OF THE INVENTION

With interconnection circuit boards according to the invention, theadhesive is applied to the wire used in scribing the conductor patternrather than to the board surface as has been the prior practice. Theadhesive is activated to a tacky state during the wire scribingoperation which forms the conductor pattern, and can thereafter be curedto permanently bond the conductors to the board surface. The technigueof this invention can be used in the initial manufacture of circuitboards or in the modification of pre-existing boards.

In the process for scribing a conductor to the surface of a substrate ina predetermined pattern, the conductor is precoated with an adhesive.Prior to the scribing step, the adhesive coating is solid, non tacky,non-blocking and preferably flexible. In the scribing step the adhesiveis activated to a tacky state using thermal, radiant, or ultrasonicenergy, or a combination thereof. The adhesive coating is capable ofrapidly reverting to a solid, non-tacky condition after activation toform a bond. The adhesive coating on at least a portion of the conductoris activated prior to, or simultaneously with, scribing the conductor.According to the process of this invention, the activated portion of theadhesive coating is placed in contact with and wets the substratesurface, reverts to a non-tacky condition and forms a bond between theconductor, which it coats, and the surface. The adhesive coating may becured to a C-stage or a thermoset condition subsequent to the scribingstep.

The adhesive coating employed for the conductors is a heat activatablecomposition which is preferably a three component formulation including:

(a) a film forming polymeric resin,

(b) a filler and/or at least one or polyfunctional compound having apolyaromatic backbone, and

(c) a curing agent non-reactive under conditions providing heatactivation of the adhesive but being capable of reacting with the othercomponents of the adhesive to cure the adhesive resin to the C-stage.

The adhesive must be non-blocking, non-tacky and preferably flexiblewhen coated on the wire, must be activatable during wire scribing toform a bond sufficient to hold the conductor pattern in place, and ispreferably curable to a C-stage to provide a permanent thermoset bond inthe final product.

The preferred technique for activating the adhesive uses pulsed laserenergy wherein the pulse repetition rate varies as a function of therate at which wire is being scribed. The pulse energy is adjusted toprovide the correct quantum of energy to activate the adhesive.Successive pulses activate adjacent or partially overlaping sectionsalong the conductor length with the number of pulses per uniform lengthbeing constant. As a result, the pulse repetition rate varies as afunction of speed and the energy applied along the length of theconductor is of the correct uniform value regardless of speed.

The interconnection circuit board according to the invention includes atleast one insulated conductor which is adhered to the surface of thesubstrate by means of a non-tacky, non-blocking adhesive coating atleast partially encapsulating the conductor. In a cross-sectional view,the outline of the adhesive coating usually forms a characteristicbell-shaped configuration over the conductor. The adhesive coating isbonded to the substrate at the points of contact between the surface andthe conductor. In the vicinity of conductor crossovers, the adhesiveforms a bond between conductors.

The process of this invention can be used to produce new interconnectioncircuit boards using standardized or nonstandardized formats. It canalso be used to modify existing interconnection circuit boards such asprinter wiring boards or discrete wire boards at any stage of theirconstruction. Modifications can be made on circuit boards either priorto or after inserting or placing components. Modifications may also bemade to circuit boards having oversized surface pads, dual surface padsor double-socketed circuit holes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a through 1d show, sequentially, perspective views of circuitboard modification.

FIG. 1a is a perspective view with partial cut-aways showing a completedinterconnection circuit board having terminal holes prior to insertionof components.

FIG. 1b is a perspective view with partial cut-aways showing of thecircuit board of FIG. 1a wherein modification conductors have beenscribed to the surface of the board according to the process of thisinvention.

FIG. 1c is a perspective view with partial cut-aways of the modifiedcircuit board of FIG. 1b with three components inserted.

FIG. 1d is a perspective view with partial cut-aways of the modifiedcircuit board of FIG. 1c after solder is placed in the terminal holes.

FIG. 1e is a perspective view with partial cut-aways of a modifiedmultiple layer interconnection circuit board showing three layers ofcircuit patterns, inserted components and a via connecting the layers.

FIGS. 2a through 2c show, sequentially, perspective views ofmodification of a surface-mounted interconnection circuit board.

FIG. 2a is a perspective view with partial cut-aways showing aninterconnection circuit board having six terminal pads prior to additionof components.

FIG. 2b is a perspective view with partial cut-aways showing the boardof FIG. 2a with two insulated conductors scribed to the surface of theboard according to the process of this invention.

FIG. 2c is a perspective view with partial cut-aways of the board ofFIG. 2b subsequent to addition of a surface-attached component.

FIG. 3a is a perspective view with partial cut-aways showing a circuitboard having six terminal holes and two surface-attached components onwhich two modification conductors have been scribed.

FIG. 3b is a perspective view with partial cut-aways showing a circuitboard having conductive surface pads modified after component placement.

FIGS. 4a through 4c show, sequentially, perspective views of fabricatingan interconnection circuit board according to the process of thisinvention.

FIG. 4a is a perspective view with partial cut-aways of a prefabricatedcircuit board format having twenty predrilled standardized metallizedterminal hole locations.

FIG. 4b is a perspective view with partial cut-aways of prefabricatedcircuit board format of FIG. 4a with two conductors scribed betweenterminal holes and soldered to said holes to makes the interconnections.

FIG. 4c is a perspective view with partial cut-aways showing the circuitboard format of FIG. 4b having a leaded component inserted into theterminal holes.

FIGS. 5a through 5c show, sequentially, perspective views of thefabrication of a non-standardized interconnection circuit board havingeight terminal holes and eight terminal pads.

FIG. 5a is a perspective view with partial cut-aways of a circuit boardpanel having terminal holes and pads which is to be scribed withconductors according to the method of this invention.

FIG. 5b is a perspective view with partial cut-aways of the panel ofFIG. 5a after three adhesive-coated conductors have been scribed betweenterminal points.

FIG. 5c is a perspective view with partial cut-aways of the panel ofFIG. 5b after components have been inserted and attached to the panel.

FIG. 6 is a cross-sectional view of a circuit board including adhesivecoated conductors ahdered to both sides of the circuit board.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, an adhesive coated conductoris scribed in a predetermined pattern on a surface of a substrate. Theadhesive is activated as the conductor is being scribed to form a bondholding the conductors in place. The circuit board is preferablythereafter cured to provide a permanent thermoset bond for the conductorpattern.

Conductor Preparation - Adhesive Coatings

The conductors used in this process are coated with a substancehereinafter referred to as the "adhesive coating" which is used to bondthe conductor to a surface. Prior to activation, the adhesive coating isnon-tacky, non-blocking and preferably flexible. These properties permithandling and manipulation of the adhesive coated conductor prior to andduring scribing. The coated conductor may be stored on a spool for easystorage and access. Furthermore, the adhesive coating, does not adhereto or leave residue which will clog the apparatus used to scribe theconductors. The adhesive coating, in its activated state, providesadhesion between the conductor and the surface of the substrate on whichthe conductor is to be scribed. It should provide sufficient strength toallow the formation and subsequent preservation of conductor inflectionson the surface.

The adhesive coatings used in the practice of this invention are able toadhere to a wide variety of materials which are used on or comprise thesurfaces of substrates useful in the interconnection circuit boardindustry. These materials include insulating and conductive surfaces,e.g. polymer resins, ceramics, glass bonded metal or carbon conductors,polymer-bonded metal or carbon powder conductors, or conductivepolymers. Examples of such materials include: dielectrics, e.g.phenolics, polyimides, epoxy-glass laminates, thermoplastics,thermosets, solder masks, such as thermally cured thermosets,ultraviolet radiation-cured materials, materials cured by multiplemechanisms, legend or nomenclature inks, and ceramics; and metallicsurfaces, such as copper, plated or reflowed solder, gold, silver,nickel, conductive inks, and thick and thin film screened conductors.Preferably, the adhesive coating is able to adhere to to these surfaces.However, an adhesive coating which adheres to a limited number ofsurface materials may also be used.

The substrate can be a blank circuit substrate or a circuit substratehaving etched foil power and ground conductors or the like, anelectronic interconnection board, including a discrete-wired circuitboard, a standard printed circuit board, a multilayer circuit board, acircuit board with components thereon or a circuit board at any otherstage of construction.

The adhesive coating should be flexible to allow the conductor to travelsmoothly through a scribing apparatus and to allow the conductor to forma variety of inflection angles.

Upon activation, the adhesive coating becomes tacky and can bond theconductor to the substrate surface. Once the adhesive coating isactivated and the conductor applied and bonded to the surface, theadhesive coating rapidly reverts to a solid, non-tacky condition. Therapid reversion to a solid, non-tacky condition does not entail anysubstantial change in the adhesive coating's conformation or volume.This reversion occurs in about 50 to 200 milliseconds which issufficiently short to allow the conductor pattern to retain dimensionalstability, thus limiting or substantially avoiding relative movement ofthe bonded conductors with respect to each other and the substratesurface.

The adhesive coating and, if present, one or more underlying layer(s) ofinsulation should be removable at the endpoints of the conductor. Whenthe insulation is removed, electrical connections can be made betweenthe scribed conductor and the terminal points. The adhesive coating andinsulation layer(s) should be able to be removed without damage to theconductor or the surface to which the conductor is bonded. This removalprocess is hereinafter referred to as "stripping".

The bond formed by the adhesive coating employed in the practice of thisinvention can withstand any subsequent processing that is typicallyperformed during the fabrication of a circuit board. It is resistant tochemicals used during manufacture, such as cleaning solutions, solderflux and the like. The bond also can withstand a variety of differentthermal environments to which the board may be subjected. The adhesivecoating is resistant to breakage or deformation caused by mechanicalstress, such as handling and manual or machine tooling.

A suitable non-tacky, non-blocking, flexible adhesive coatingcomposition comprises:

(a) a first component comprised of a film forming polymeric resin (1)having an average molecular weight (M_(w)) between about 10,000 andabout 100,000 and (2) having an epoxide, hydroxyl or unsaturatedfunctionality greater than 2, said polymeric resin being selected fromthe group consisting of polyesters, polyurethanes, polyethers, epoxies,allyl polymers and acrylics;

(b) a second component selected from the group consisting of a filler,polyfunctional compounds and mixtures thereof, said polyfunctionalcompounds having an average molecular weight below about 7,000 andcontaining a polyphenol backbone, the weight ratio of said firstcomponent to said second component being between about 1.5:1 and about9:1; and

(c) a curing agent which is capable of reacting or initiating a reactionwith the functional groups of the polymeric resin to form crosslinks andcure the polymeric resin to a C-stage upon application of sufficientenergy in the form of heat or radiant energy, said curing agent beingnon-reactive or blocked at the temperatures reguired to activate theadhesive composition, said curing agent being present in an amountsufficient to C-stage the polymeric resin; said composition beingflexible, and in the C-stage capable of forming an infusible compositionwhich does not melt, flow or decompose when exposed for 10 seconds tomolten solder at 260° C. and does not soften when exposed todichloromethane at 25° C. for 10 seconds.

The adhesive may also be a solid adhesive composition which isthermosetting and can be activated upon application of sufficient heator ultrasonic energy without thermosetting, such a compositioncomprising:

(a) a first component comprised of a film forming polymeric resin havinga hydroxyl functionality greater than 2 and selected from the group ofpolyols consisting of polyesters, polyurethanes, polyethers, epoxies,and combinations thereof, said resin having been reacted to the B-stagewith a first curing agent which was present either in less than astoichiometric quantity or was capable of reacting with functionalgroups that were present at low concentrations on the polymer chain,said curing agent being a polyisocyanate and having been present in anamount sufficient to react with 10 to 60 percent of the hydroxyl groupsto B-stage the polymeric resin sufficiently to provide the compositionwith non-blocking properties; and

(b) a second component selected from the group consisting of a filler,polyfunctional compounds and mixtures thereof, said polyfunctionalcompounds having an average molecular weight below about 7,000 andcontaining a polyaromatic backbone, the weight ratio of said firstcomponent to said second component being between about 1:5:1 and about9:1 and

(c) a C-stage curing agent which is capable of initiating a reactionwith the hydroxyl groups of the polymeric resin to form crosslinks andcure the polymeric resin to a C-stage upon application of sufficientenergy in the form of heat or light, said second curing agent beingnon-reactive or blocked at the temperatures required to activate theadhesive composition; said composition being flexible, and in theC-stage capable of forming an infusible composition which does not melt,flow or decompose when exposed for 10 seconds to molten solder at 288°C. and does not soften when exposed to dichloromethane at 25° C. for 10seconds.

Another adhesive coating composition which can be used comprises:

(a) a film forming epoxy resin having been reacted to a B-stage polymerhaving an average molecular weight, greater than about 30,000;

(b) a polyfunctional resin having an average molecular weight belowabout 5,000 and containing a polyphenol backbone, the weight ratio ofsaid first component to said second component being between about 1:1and about 3:1; and

(c) a curing agent which is capable of reacting or initiating a reactionwith the functional groups of at least one of the resins to formcrosslinks and cure the resin to a C-stage upon application ofsufficient energy in the form of heat or radiant energy, said curingagent being non-reactive or blocked at the temperatures required toactivate the adhesive composition, said curing agent being present in anamount sufficient to C-stage the resin; said composition being flexible,and in the C-stage capable of forming an infusible composition whichdoes not melt, flow or decompose when exposed for 10 seconds to moltensolder at 260° C. and does not soften when exposed to dichloromethane at25° C. for 10 seconds.

The adhesive coatings may be thermoplastic or thermosetting. The coatingmay be composed of a homopolymer, a copolymer or a blend of polymers.Additives may be included that impart the capability of partially curingthe adhesive coating in advance of conductor placement and final curingof the adhesive coating after scribing.

Homopolymers and copolymers used in the process of this invention mayhave thermoplastic properties. For example, high molecular weightpolyesters (molecular weight of between about 5,000-25,000, preferablybetween about 15,000-20,000), high molecular weight polyurethanes(molecular weight of about 3,000-15,000, preferably about 7,000-12,000),and polyolefins, and the like may be used as thermoplastic adhesivecoatings in this invention.

Thermosetting polymers may be used in a partially-cured or B-stagedstate in the adhesive coatings in the process of this invention. Forexample, high molecular weight epoxy and phenoxy resins may be used.Urethane acrylates, polyesters, and acrylated epoxies having a molecularweight of between about 600 and 1100 and other epoxies having an epoxideeguivalent weight of between about 1,000 and 2,000 and the like may beused. Novolac or resole phenolic resins having a molecular weight ofbetween about 800 and 1500 are also useful in the process of thisinvention. Novolac epoxies are particularly useful in applicationsinvolving high-temperature exposure. When epoxy resins are used, it maybe necessary to reduce their surface tension with flow modifiers,surfactants and fillers. Epoxy curing agents such as polyamide may beused to partially cure the epoxy and render the coating non-tacky.Polyimides may also be used in the adhesive coating in the process ofthis invention.

Partially-cured, or B-staged, polymers which can be cross-linked by ablocked curing agent, e.g. blocked isocyanate, can also be used. Thesepolymers can be B-staged at a temperature higher than that used to coatthe conductor.

Copolymer and polymer blends can be used in the process of thisinvention to make adhesive coating material. Further, partial curing maybe accomplished with a single curing agent if the polymers are carefullychosen to contain the same type of reactive group. Examples ofcopolymers useful in the process of this invention are high molecularweight hydroxy-containing polyester copolymerized with a high molecularweight hydroxy-containing epoxy by reaction with an isocyanate. Anotherpolymer blend useful in the process of this invention is a blend of ahigh molecular weight (about 20,000) hydroxy containing polyester and alow molecular weight (about 2,500) hydroxy containing polyestercopolymerized with an isocyanate.

Free radical polymerization post-curing of the adhesive coating can beachieved using appropriate curing agents. For example, free radicalpolymerization using ultraviolet light can be accomplished byincorporating into the adhesive coating composition2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenylketone orthe like. Thermal free radical polymerization can be accomplished byincorporating 1,1'-azobis (cyclohexane carbonitrile), dicumyl peroxide,1,1'-bis(tert butylperoxy)-di-isopropylbenzene or the like into theadhesive coating composition. Electron beam curing agents can also beused for free radical polymerization.

Fillers may be added to an adhesive coating composition in order toimprove its non-blocking properties prior to use. Fumed silica(commercially available as Cab-O-Sil™ from Cabot Corporation), talc,titanium dioxide and the like may be used for this purpose.

Other compositions used in the adhesive coating of this invention areset forth in copending patent application entitled "Heat ActivatableAdhesive For Wire Scribed Circuits" (Schoenberg et al.) which isincorporated herein by reference.

The adhesive coating may be made up of two or more layers. One layer maybe an adhesive and the other layers may serve other functions. Forexample, an adhesive layer may be applied to the conductor and aprotective outer layer may be applied over it which can be dissipated byexposure to an energy source. The outer dry coating allows handling andspooling. The inner coating may be tacky with surface wettingcharacteristics. An energy source such as a laser may be used to meltthe outer coating and expose the tacky material to the substrate surfacefor bonding. In another embodiment, the coating may containmicroencapsulated regions of low viscosity, such as cyanoacrylate, thatcan be released on exposure to pressure. When the encapsulated regionsopen, the adhesive properties of the coating are activated. Afterscribing, the adhesive coating is cured to render it non-tacky.

A number of techniques are known which are suitable for applying theadhesive coating to conductors. For example, the conductor may bedragged through a felt material soaked with a very low viscosityadhesive coating composition. Uniform concentric layers of coating maybe formed by orienting the conductor in random directions and passing italong the felt several times.

The die extrusion technique for applying the adhesive coating consistsof passing the conductor through a drawing die. On one side of the dieis a reservoir of viscous adhesive material. The conductor is drawnthrough the reservoir and then through the die. Adhesive material coatsthe conductor as the conductor is drawn through the die. The hydrostaticaction of the adhesive material acts to center the conductor in the diesuch that an even coating is formed around the circumference of theconductor. Once the coated conductor leaves the die, the coating isexposed to heat in order to drive off solvents.

Adhesive Activation And Curing

The adhesive-coated conductor can be scribed to the surface of asubstrate. During the scribing process of this invention, the conductorpreferably is automatically placed on and bonded to the substratesurface along a predetermined path. The substrate surface preferably ismounted on a movable work table. The conductor is fed to the substratesurface from a scribing head assembly. The conductor is laid on thesubstrate surface by moving the work table relative to the scribing headassembly and by rotating a scribing head assembly in the direction oftable movement. The wire scribing head assembly and the table movementare preferably numerically controlled.

As the conductor is fed toward the surface, and just prior to itsreaching the surface, the portion of the conductor's adhesive coatingwhich is to be placed in contact with the surface is activated. Theconductor itself should not be affected by the adhesive activatingenergy. The conductor is brought into close proximity with the substratesurface subsequent to or simultaneously with activation. The activatedportion of the adhesive coating contacts and adheres to the substratesurface, forming a bond between the conductor and the substrate surface.

The energy used for activating the adhesive coating should becontrollable in magnitude and intensity. The level of the energy shouldbe sufficient to activate the adhesive, but not to damage the conductoror the substrate surface. Thermal, ultrasonic or radiant energy sources,or combinations thereof, may be used. The adhesive may be activatedchemically using a solvent directed at a portion of the adhesivecoating. Alternatively, heated or superheated gasses such as air may bedirected at the coating to supply thermal energy to activate theadhesive.

Radiant energy sources which can be used in the practice of thisinvention include laser, and focused infrared radiation. The activatingsources may be used alone or in combination.

The preferred activating energy source is one or more laser beams. Theenergy output and spot size of the laser beams is controllable. A laserbeam may be directed at a selected portion of the adhesive coating onthe surface of the conductor needed to form a bond with the substrate. Amultiplicity of energy beams (which can include lasers, different typesof lasers or other beams) or beam splitting techniques can be provided.One energy beam may be used for activating the adhesive coating whileanother energy beam may be used for other purposes such as stripping orsoldering.

In order to activate the adhesive coating, an energy beam, preferably alaser beam, is directed to a point on the conductor at or before theprojected point of contact between the conductor and the substratesurface. The adhesive coating is activated at or prior to contacting thesubstrate surface such that it is in a tacky state when the conductorcontacts the surface.

Preferably, a laser beam is used for activating the adhesive coating;more preferably, a CO₂ laser beam which emits infrared radiation shouldbe used. The laser energy should be directed at the desired requisitearea on the adhesive coating i.e. the underneath portion adjacent thesubstrate contact point, and discharged in the form of a pulsed beam.The pulses can be created by interrupting the emission of a continuouswave laser beam by turning the power on and off, or by "Q-switching"using electro-optic or mechanical shutters or acousto-optic couplers.

The laser beam pulses are preferably uniform pulses with an energycontent adjusted for existing conditions (e.g. beam focus, adhesiveactivation requirements etc.) so the energy is sufficient to activatethe adhesive without damaging the conductor or surrounding surfaces.Therefore, the product of the pulse amplitude (energy level), and pulsewidth, (pulse duration) should be constant. The "spot size" should bechosen as the minimum diameter large enough to allow easy alignment withthe conductor. Larger spot sizes diffuse energy due to the Gaussianenergy distribution of the beam and, hence, are undesirable. The pulsesare preferably discharged at such a rate that the spots partiallyoverlap on the conductor so as to expose and activate the adhesivecoating efficiently and evenly. In other words, a pulse should beemitted each time a predetermined length of conductor is traversed.

Once spot size has been chosen, pulse amplitude and pulse width areadjusted to produce sufficient energy to activate the exposed area ofadhesive coating without damaging surrounding surfaces. The adjustmentof the pulse energy content also takes into account conditions such aslaser efficiency, wire size, and the particular adhesive requirements.Since the number of pulses is constant per uniform length, the pulserepetition rate is a function of the speed at which the wire is beingscribed.

If a 20-watt continuous-wave CO₂ laser is used, and the scribing speedis between about 200 and 600 inches/minute, the pulse width selectedshould be about 200 to 2000 microseconds, pulse repetition rate aboutone pulse per 0.10 to 0.25 mm (0.004 to 0.010 inches) and the spot sizeselected should be from about (0.5 to 2.5 mm (0.020 to 0.100 inches) indiameter. If wire handling equipment is fast enough, bonding speeds ashigh as 1000 inches/minute can be achieved. Additional informationregarding pulsed laser adhesive activation is included in copendingapplication "Method of Manufacturing Interconnection Circuit Boards"(Morino et al).

Scribing speed may vary often and considerably during the scribingprocess. When the scribing process begins, there is an acceleration torunning speed, during which time the velocity varies constantly; ifthere is an inflection point along the path of the conductor, there is adeceleration to a stop while the inflection is made and subsequentacceleration to running speed. If the energy dispensed to the adhesivecoating were not varied according to variations of scribing speed, theactivation of different areas along the adhesive coating of theconductor would be inconsistent. Emission of a fixed number of constantenergy pulses per uniform length of movement obviates these problems.Each unit area of the conductor receives the same amount of energyregardless of the scribing speed.

After contact of the conductor and adhesive coating with the substratesurface the adhesive coating loses energy and reverts to a solidnon-tacky condition thus bonding the conductor to the substrate. Theconductor is scribed between terminal points in this fashion.

After the conductor pattern is fixed onto the substrate, a separatecuring step may be performed. The coating may be cured by baking,exposure to heat, ultraviolet radiation and the like. The adhesivecoating of the scribed conductors preferably includes a curing agentwhich is non-reactive under conditions that activate the adhesive duringthe scribing operation but which can be made reactive to provide apermanent thermoset bond at higher termperatures or by applyingultraviolet radiation.

EXAMPLE 1

An elongated preformed wire conductor, for example, a copper wire of 38awg (American Wire Gauge, or 0.1 mm diameter) plated with approximately0.5 micrometers of silver is covered with a layer of polyurethaneinsulation, 38 micrometers thick. The conductor is further provided withan adhesive coating having the following dry weight composition: 100 ghigh molecular weight polyurethane acrylate, 15 g epoxy acrylate, 9.8 gof a polyisocyanurate of toluene di-isocyanate, 3.5 g ultraviolet curingagent, and 0.5 g 4-methoxyphenol.

The corresponding wet weight composition, ready for coating, is asfollows: 333.3 g high molecular weight polyurethane acrylate (32%solution), 15 g epoxy acrylate, 19.6 g polyisocyanurate (50% solution),3.5 g ultraviolet curing agent, 0.5 g 4-methoxyphenol and toluene in theamount of 7 weight percent of the total.

The adhesive coating composition is applied to the insulated conductorby repeatedly passing the conductor through the wet adhesive coatingcomposition and a series of diamond dies of increasing diameter. Thefirst diamond die in the series is provided with an orifice 152micrometers in diameter. The next die which the conductor is to passthrough is provided with an orifice 6.4 micrometers larger in diameterthan the first. The wire conductor is passed through the wet adhesivecoating composition, then through a diamond die, then an oven to removeresidual solvents from the applied adhesive coating. This process isrepeated with dies having increasingly larger orifices until theconductor diameter is 266.7±5.1 micrometers (0.0105±0.0002 inches). Thewire conductor is then spooled for storage. The adhesive is sufficientlyflexible to allow radii of bending in the range of 0.12-0.25 mm. Afterthe wire conductor is scribed in a predetermined pattern on the surfaceof a substrate, the adhesive coating can be cured by exposure to anultraviolet light source of at least 15 joules/cm².

EXAMPLE 2

A wire conductor is coated in accordance with the method described inExample 1 with an adhesive coating having the following dry weightcomposition: 100 g Adcote™ 76P1 (polyester having molecular weight ofabout 25,000 available from Morton Chemical Co.), 30 g blockedisocyanate commercially available as Desmodur VP KL5-2371 available fromMobay Chemical Corporation, 7.5 g fumed silica (commercially availableas Cab-O-sil™ from Cabot Corp.), 5 g zirconium silicate, 1.5 g orangepigment and 20 g methylethyl ketone (MEK) solvent and having a wetweight composition of 192.3 Adcote 76P1 and 40 g blocked isocyanate, 7.5g Cab-O-sil™, 5 g zirconium silicate, 1.5 g orange pigment and 20 g MEK.

The adhesive coated wire conductor is fed through a wire scribing head.The substrate on which the conductor is to be scribed is a standardprinted circuit board having on its surface etched areas where copperhas been etched to leave epoxy, a copper conductor pattern and soldermask. As the conductor is fed through the scribing head, a stream of hotair having a temperature of about 120°-150° (250°-300° F.) is aimed atthe conductor in order to activate the adhesive coating. The hot airstream is aimed at a point on the conductor which will melt and contactthe surface. The adhesive coating remains melted and, therefore,activated for approximately 0.5 seconds. The scribing speed is about 13mm (0.5 inches) per second. The hot air stream is therefore aimed at apoint on the conductor approximately 1.5 mm (0.060 inches) above thesurface, allowing the adhesive coating to melt continuously as theconductor is continuously fed through the scribing head and through aroller. The roller serves to impress the conductor onto the surface. Theadhesive coating is still fluid when the conductor contacts the surface.The adhesive coating resolidifies and become non-tacky within about onesecond, thus bonding the conductor and maintaining its positionalstability. After the conductor has been scribed in the predeterminedpattern, the adhesive coating is fully cured by baking in an oven at atemperature of 150° C.

EXAMPLE 3

A wire conductor coated with the adhesive coating described in Example 2is scribed to the surface of an epoxy gloss laminate substrate asdescribed in Example 2. However, instead of using a hot air stream toactivate and melt the adhesive coating, an ultrasonic transducer is usedas the activating energy source. The ultrasonic system includes anultrasonic generator, a power supply, a coil, a transducer, feedbackelements and a stylus tip. The conductor is fed through the scribinghead and the stylus tip, which has a groove under which the conductorfits. The ultrasonic transducer produces mechanical vibrations at a rateof about 25,000 Hz. These vibrations are converted into heat, whichmelts the adhesive coating not only at the point of contact between thestylus and the conductor, but at the point between the conductor and thesurface. The melted adhesive coating adheres to the board as it contactsthe surface.

EXAMPLE 4

A wire conductor coated with the adhesive coating described in Example 1is to be scribed onto a printed circuit board in accordance with themethod of Example 2. However, a laser energy source is used rather thana hot air stream. A Laakman Electro-Optics, Inc. Model RF 165 laser isused as the laser energy source. The model RF 165 is a sealed CO₂ laserhaving a radio frequency-excited waveguide, a power output of 20 wattsCW (continuous wave), a Gaussian (TEM_(oo)) beam shape and a maximummodulation frequency of 10 KHz.

The laser energy is discharged at the wire conductor in the form of apulsed beam. The pulse width of the beam is about 200 microseconds. Thepulse amplitude of the beam is about 20 watts. The spot is approximatelycircular and has a diameter of about 1 mm (0.040 inches). The beam ispulsed when the conductor has been scribed about 0.2 mm (0.008 inches).The scribing speed is about 5 meters (200 inches) per minute. The spotsize and pulse frequency are adjusted so that each section of conductorreceives about five laser pulses. The activated adhesive coating iscontacted with the surface of the substrate and the adhesive coatingloses energy, becomes non-tacky and forms a bond with the surface withinabout 200 milliseconds. When all conductors of the predetermined patternhave been scribed to the board, the adhesive coating is fully cured byexposure to ultraviolet light.

EXAMPLE 5

A wire conductor coated with an adhesive coating is scribed to thesurface of a substrate according to the procedure of Example 4. However,the adhesive coating is a mixture of 100 g dry weight or 166.67 as wetweight Purelast™ 2195 polyether having carboxyl groups adducted onto thepolyether backbone and crosslinked with toluene di-isocyanate (availablefrom Polymer Systems Corporation), 166.7 g propyleneglycolmonomethylethyl acetate (PMA) and 25 g MEK. The wire conductor iscoated in accordance with the method described in Example 1.

EXAMPLE 6

A wire conductor is coated with the adhesive coating composition ofExample 1 in accordance with the method described in Example 1. Theadhesive coating of the conductor is activated in accordance with themethod described in Example 4. However, the conductor is scribed to thesurface of a previously fabricated discrete wire interconnection boardover existing wires and between two terminal points in order to modifythe interconnections on the board.

EXAMPLE 7

A heat activated adhesive was prepared with a blend of a B-stagedpolymer of a high molecular weight allylic urethane and a B-staged epoxyacrylate. The B-stage mechanism is the reaction of polyisocyanurate withthe hydroxyl groups of both polymers. An ultraviolet initiated, freeradical curing agent was incorporated in the blend to enable completecuring to a C-stage composition through the allylic and acrylic groupson the polymers. The adhesive was prepared from the formulation below.

    ______________________________________                                        Component                   dry solids                                        ______________________________________                                        Polyurethane resin 32% in butanone, the polymer                                                           315 g                                             was hydroxyl terminated with allylic groups                                   evenly spaced the polymer chain; the repeating                                molecular weight was approximately 1000 and                                   the hydroxyl no. was 11.3 mg KOH/g (commercially                              available as S126-224 ™ from Bostick Div. of                               Emhart Chemical Group, Middleton, MA.)                                        Bisphenol A epoxy diacrylate ester with a                                                                  15 g                                             weight of 834 (commercially available as                                      CMD 3703 ™ from Celanese Specialty Resins,                                 Louisville, Kentucky.). The chemical formula                                  is believed to be                                                             CH.sub.2 = CH--CO--[O--CH.sub.2 --                                            CHOH--CH.sub.2 --O--C.sub.6 H.sub.4 --                                        C(CH.sub.3).sub.2 --C.sub.6 H.sub.4 --O--CH.sub.2 --                          CHOH--CH.sub.2 --O--C.sub.6 H.sub..sub.4 --                                   C(CH.sub.3).sub.2 --C.sub.6 H.sub.4 --O--CH.sub.2 --CHOH--CH.sub.2 --         CH.sub.2 --].sub.2 --O--CO--CH = CH.sub.2                                     Polyisocyanurate of toluene diisocyanate 50%                                                              19.6 g                                            in butyl acetate (commercially available from                                 Mobay Chemical Corp, Pittsburgh, PA as                                        Desmodur IL ™                                                              2,2-dimethoxy-2-phenylacetophenone                                                                         2.5 g                                            (commercially available as Irgacure 651 ™ from                             Ciba-Geigy Corp.)                                                             4-methoxyphenol toluene      0.5 g                                            7% by weight of the total formulation                                         ______________________________________                                    

The diacrylate epoxy ester (15 g) was reacted with polyisocyanuratesolution (9.6 g) for 3 hours at 95° to B-stage the epoxy acrylate resinby crosslinking the hydroxyl groups. This produced a B-stage epoxyacrylate polymer with an average molecular weight of 5400.

The allylic polyurethane resin was reacted with 10 grams ofpolyisocyanurate solution for 1 hour at 95° C. This polymerized resin toa B-stage polymer with an average molecular weight of

The two B-stage polymers were combined and refluxed for 1 hour at 95° C.Butanone was added as necessary to control viscosity.

After refluxing the B-stage polymers together, the solution was cooledand 3.5 grams of 2,2 -dimexthoxy 2-phenylacetophenone and 0.5 grams of4-methoxyphenol dissolved in 30 grams of butanone were added to thepolymers. The weighing dish used to weight the 2,2-dimethoxy-2-phenylacetophenone and 4-methoxyphenol was washed three times with 20grams of butanone and the wash solvent was also added to the polymersolution. The solution was then mixed thoroughly for 30 minutes andweighed. 7% by weight toluene was added, and then the solution was mixedfor an additional 30 minutes.

Copper wire 0.1 mm in diameter covered with a layer of polyurethaneinsulation to a diameter of 0.14 mm was coated with a uniform layer ofadhesive by passing the wire repeatedly through the adhesive solution,drawing the wire through a diamond die and passing it through an oven todry the coating and remove residual solvents. For each repetition of theprocess the diamond die was of larger diameter. The first die was 0.152mm diameter and the diameter of each succeeding die was 0.0063 mm largerthan the previous die. The coating process was continued until theoutside diameter of the wire with the dry, heat activated adhesivecoating was 0.26 mm to 0.27 mm. The wire was coated and stored in areaswhere ultraviolet light was excluded. The wire was wound on a spool forstorage until use. The heat activated adhesive coating on the wire didnot block in storage.

The wire coated with the heat activated adhesive was wire scribed toprinted wiring boards to modify the conductive pattern. During thescribing process the wire was automatically placed on and bonded to thesurface of the printed wiring board. The surface of the printed wiringboards comprised solder mask areas, epoxy substrate areas and exposedmetal areas. The printed circuit was mounted on a moveable work table.The wire was fed out on the printed wiring board surface from a scribinghead assembly. The wire was laid on the substrate by moving the worktable relative to the scribing head assembly and by rotating a scribingfeed mechanism in a predetermined direction. The wire scribing headassembly and the table were numerically controlled.

As the wire was fed toward the surface, and just prior to its reachingthe surface, the portion of the heat activatable adhesive coating whichwould contact the surface was exposed to a beam from a CO₂ laser (ModelRF 165™ from Laakman Electro-optics, Inc.). The laser was a sealed CO₂laser with a radio frequency excited wave guide, a power output of 20watts CW (continuous wave), a Gaussian energy distribution, and amaximum modulation frequency of 10 kHZ.

The laser energy was discharged at the wire in the form of a pulsedbeam. The pulse amplitude of the beam was about 20 watts. The spot wasapproximately circular and had a diameter of about 1 mm. The beam waspulsed when the wire had been scribed about 0.2 mm. The scribing speedwas about 5 m/min. The spot size and pulse frequency were adjusted sothat each section of heat activatable adhesive coated wire receivedabout five overlapping laser pulses. The activated adhesive coatingcontacted the surface of the printed wiring board and the adhesivecoating became nontacky and formed a solid bond with the surface inabout 200 milliseconds.

The wire was securely bonded by the heat activated adhesive to thesolder mask, epoxy substrate and exposed metal areas as well as to otherscribed wires. When all the wires to modify the conductive pattern hadbeen scribed to the printed wiring boards, the boards were exposed to19.5 joules/cm² of ultra violet light to cure the heat activatedadhesive to the C-stage.

Printed wiring boards with the wire scribed conductors were soldered at265° C. for 10 seconds. There was no failure of the adhesive bondbetween the wires and the substrate, and no visible evidence of attackon or damage to the adhesive coating. Printed wiring boards with wirescribed conductors were placed in dichloromethane for 10 seconds, driedin air at ambient temperature for 10 minutes and examined with the aidof a microscope. There was no failure of the adhesive bond between thewires and the substrate, and no pitting, crazing or other indication ofattack on the adhesive coating.

EXAMPLE 8

A heat activatable adhesive was formulated from a polyester resinbelieved to have a molecular weight of about 20,000 and a hydroxylfunctionality of 2, and a blocked isocyanate for a C-stage or the finalcure. The ratio of resin to blocked isocyanate was 10:3. The formulationis as follows:

    ______________________________________                                        Component                   weight                                            ______________________________________                                        Polyester adhesive resin with dihydroxy                                                                   192 g                                             functionality and average molecular weight of                                 20,000 prepared from isophthalic acid and a nine                              carbon dibasic acid esterified with ethlene glycol                            and diethylglycol as a 51% solution in butanone                               commercially available as Adcote 761 ™ from                                Morton Chemical Corp.)                                                        Blocked aliphatic isocyanate which will unblock                                                            40 g                                             100-110° C. (The blocked polyisocyanate is 75% solids                  dissolved in a 50/50 mixture of xylene and                                    2-ethoxyethylacetate commercially available from                              Mobay Chemical Corp., Pittsburgh, PA as                                       Desmodur VP KL 54-2371 ™.).                                                Fumed silica (commercially available from Cabot                                                            7.5 g                                            Corp., Tuscola, IL as CAB-O-SIL ™)                                         Zirconium silicate powder average particle size 0.55                                                       5 g                                              micrometers (commercially available from TAM                                  Ceramics Inc., Niagara Falls, NY as Excelopax ™.)                          Fluorescent pigment (commercially available as Day-                                                        1.5 g                                            Glo Orange ™ from Day-Glo Color Corp., Cleveland, OH)                      ______________________________________                                    

The ingredients were milled together on a three roll paint mill anddiluted with 20% solids with methyl ethyl ketone for coating on wire.

Insulated wire 0.14 mm in diameter with a copper core 0.1 mm in diameterwas overcoated with a layer of the heat activatable adhesive and driedwith forced hot air. The application of adhesive was repeated until thediameter of the wire plus the heat activatable adhesive was increased to0.27 mm (at least 85% larger than the original diameter).

The heat activable adhesive coated wire was scribed onto the surface ofan glass cloth reinforced epoxy laminate type FR-4 using a numericallycontrolled wire scribing head assembly and work table similar toExample 1. A hot air jet (air heated to a temperature of 120° to 150°C.) was used to activate the adhesive layer instead of the laser beamused in Example 7, and the roller on the scribing head was used to placethe activated adhesive coated wire in contact with the FR-4 surface asin Example 7.

After wire scribing the FR-4 laminate was heated to at least 120° C. tocrosslink the adhesive forming an infusible bond between the wire andthe FR-4 laminate capable of withstanding molten solder at 288° C. for10 seconds. The laminate was heated in three stages to crosslink theadhesive: 45 minutes at 85° C., 45 minutes at 12° C., and 45 minutes at155° C.

The wire scribing is repeated except that instead of activating theadhesive layer with a laser beam or a hot air jet, the adhesive layer isactivated ultrasonically. The ultrasonic system includes an ultrasonicgenerator, a power supply, a coil, a transducer, feedback elements and astylus tip. The heat activatable adhesive coated wire is fed through thescribing head and the stylus tip, which has a groove under which theadhesive coated wire fits. The ultrasonic transducer produces mechanicalvibrations at a rate of about 25 kHz. These vibrations activate theadhesive coating and adhere the wire to the FR-4 substrate.

EXAMPLE 9

A heat activated adhesive coating composition was prepared based on adiacrylate ester of a diepoxy bisphenol A resin combined with a solidexpoxy resin. The diacrylate ester resin was CMD 3703™. The solid expoxyresin (EpiRez 540C™ commercially available from Celanese Coatings andSpecialities Co.) had an epoxy equivalent weight of 1600.

In order to make a non-blocking adhesive formulation, the molecularweight of the epoxy resin was increased from about 3,200 to over 35,000by reacting it with a polyamide curing agent. Similarly, the molecularweight of the diacrylate ester (CMD 3703) was modified with 3 grams of apolyisocyanurate (Desmodur IL™) per 100 grams of epoxy acrylate ester topartially cure or B-stage the system and increase the molecular weightfrom 830 to about 5,500. The expoxy acrylate ester and thepolyisocyanurate were refluxed at 80° C. for 30 minutes to B-stage theepoxy acylate ester before adding the other components of the adhesive.

A free radical initiator was also added to the heat activated adhesiveformulation to cure the adhesive to the C-stage after it has been usedto bond scribed wires to a board. For thermal curing, dicumyl peroxidewas added. Dicumyl peroxide generated free radicals at temperatures inexcess of 150° C. For ultraviolet light curing,2,2-dimethoxy-2-phenylacetophenone was used as a free radical generator.The adhesive was refluxed at 80° C. for 30 minutes to B-stage theadhesive before coating the wire.

The final formulation was:

    ______________________________________                                        Component                   weight                                            ______________________________________                                        Epoxy diacrylate ester (CMD 3703)                                                                           40 g                                            Diglycidyl ether of bisphenol A, expoxy equivalent                                                          60 g                                            weight 1600 (EPIREZ 540C)                                                     MODAFLOW ™ (a flow promoter commercially available                                                     1.3 g                                             from Monsanto Co., believed to be a low molecular                             weight butyl acrylate)                                                        FLUORAD 430 ™ (a perfluorinated surfactant                                                             0.3 g                                             commercially available from 3M Corp.)                                         Polyamide curing agent with an approximate                                                                  5 g                                             equivalent weight of 140, believed to be the reaction                         product of 3 moles of linoleic acid dimer and 4                               moles diethylene triamine (commercially available                             from Shell Chemical Co. as Epon V-40 ™)                                    Polyisocyanurate, 50% solution (DESMODUR IL ™)                                                         1.2 g                                             Dicumyl peroxide            0.5 g                                             2,2-dimethoxy-2-phenylacetophenone                                                                        2.5 g                                             (IRGACURE 651 ™)                                                           4-methoxyphenol             0.5 g                                             ______________________________________                                    

This composition was dissolved in methyl ethyl ketone to make a solutionwith 20 percent solids. The solution was applied to an insulated wirewith an outside diameter of 0.14 mm, and the adhesive coating was driedwith forced air at 65° C. the overall diameter of the wire was increasedto 0.23 mm (64%). The heat activatable adhesive coated wire was scribedto an FR-4 substrate with hot air jet activation, as in Example 2. Theadhesive bond of wire to the substrate was much lower than Example 2.

Wires coated with the same adhesive solution to obtain a overalldiameter of 0.26 mm (85% increase). Good adhesion was obtained byscribing wire of 0.26 mm diameter, showing that heavier coating ofadhesive on the wire is preferable to achieve superior bond of scribedwires to the substrate.

EXAMPLE 10

A length of 34 awg copper wire (0.16 mm in diameter with 0.02 mminsulating layer) was drawn through a reservoir of a moltenthermoplastic adhesive, hot melt glue (Instaweld™ 34-3131 commerciallyavailable from National Starch and Chemical Corporation). The wire wasthen drawn through a die having a diameter of about 0.3 mm which cooledand soldified the adhesive coating. The wire was then heated.

The adhesive coated wire was scribed to a substrate of epoxy glass inaccordance with the procedure set forth in Example 2 except that the hotair stream was maintained at a temperature of between 350° and 450° F.The conductor bonded well to the epoxy glass.

EXAMPLE 11

The strength of the bond between the adhesive coating of a conductor andthe substrate surface to which it was bonded was measured using anInstron machine Model 1130. The measurement was performed using acontinuous vertical perpendicular peel. The vertical speed of the peelwas 10 in/minute. A ten-pound load cell was used. The sensitivitysetting of the machine was 0-1 pound and the strip chart was calibratedsuch that 0-10 on the chart represented 0-1 pound. A wire conductorhaving an adhesive coating of the formula of Example 5 was scribed to aVacrel solder mask using a CO₂ laser which was pulsed once every 6thousandths of an inch. The adhesive coating was fully cured withultraviolet light. The average peel strength of the bond was found to be40 grams in a straight line. Generally, the peel strength of theadhesive coating after full cure should be between about 30-60 grams ina straight-line scribed conductor.

Wire Stripping

When the conductor is an insulated metallic wire, electrical andmechanical terminations are made at each terminal points on thesubstrate. The metal core of the insulated wire is exposed in order tomake the termination. The adhesive coating and insulation layers arestripped to expose the conductive portion.

Selected portions of an insulated wire may be stripped of coating orinsulation by mechanical stripping, using two opposing knife edgesbrought close enough together to penetrate the conductor coatingswithout damaging the conductive portion of the conductor. The knivesthen slide along the conductor to scrape off excess material. Anothertechnique used for mechanical stripping is an abrasive jet: abrasiveparticles are sprayed at high velocity in a concentrated stream on theconductor to remove the insulation layer and adhesive coating.

A conductor's insulation layer and adhesive coatings may be chemicallystripped using a solvent. Excess solvent is preferably removed afterstripping.

Other stripping methods include low temperature and high temperaturethermal stripping. These methods include localized short term exposureof the conductor coatings to relatively high temperature energy sources.Some examples of high temperature energy sources include lasers,electrical arcs, and flame sources such as torches and the like.

Preferably, adhesive coating and insulation stripping is accomplishedwith a laser beam. The energy of the impinging laser beam strips theconductor, vaporizing the coatings. There are at least two methods ofremoving the adhesive coating and insulation layer using laser energy.According to a first laser method, a laser beam with a spot size largein comparison to the diameter of the conductor is aimed and pulsed atleast once at the section of the adhesive coating to be removed.Although the large spot size results in a relatively large area forstripping, the laser energy may be so diffuse along the outer edges ofthe spot that it may not be sufficient to vaporize completely theadhesive coating and insulation layer. Increasing the duration of thelaser beam radiation for better vaporization may cause heat conductionalong the conductor, causing the adhesive coating to bubble and boilbeyond the irradiated area. This method may also entail damage to theenvironment surrounding the conductor due to the large area of the spot.Equipment, surrounding conductors and portions of the substrate surfacemay be damaged.

According to a second more preferred laser method, a small spot isscanned along a predetermined length of conductor by moving the laserbeam along the stationary conductor or by moving the conductor, keepingthe beam stationary, or moving both. This results in a higher energyconcentration for the same laser output power. This method appears toremove the coatings more efficiently leaving a cleaner metal surface.Preferably, the diameter of the spot is approximately five times thediameter of the conductor if a CO₂ laser beam is used. Further, thefrequency of the scanning can be adjusted according to the differentmaterials to be removed. A vacuum may be used to remove debris such asfillers. A gas jet is preferably employed to blow off the residue lefton the conductor. The laser stripping process is preferably coordinatedwith the table motion to provide a predetermined cleaned length inconcert with that motion.

A reflector placed on the side of the conductor opposite the side fromwhich the energy is discharged can be used to strip the far side of theconductor. Alternatively, multiple laser beams can be aimed at opposedsides of the conductor or the conductor can be rotated to removeadhesive coating and insulating layer all around the conductor. Energycan be conducted through the conductor to remove the adhesive coatingand/or insulation layer.

An infra-red laser may be used for stripping However, an Excimer™ lasersource emitting ultraviolet radiation is also suitable in the strippingprocess. A laser beam from an Excimer laser source can vaporize theorganic materials coating the wire conductor in a process termed"photodecomposition" without affecting the conductor.

After the conductor endpoints are stripped, they can be electrically andmechanically connected to a terminal point. Termination of the conductorcan be accomplished according to any method known to those of skill inthe art. Terminal points can be surface pads, holes or apertures with orwithout metallized walls, conductive cavities, component leads,conductive fingers or the like. Surface pad termination may be used tointerconnect surface attached components, or to modify circuit boardshaving circuit holes in which the holes are already filled with solder.Termination of a scribed conductor to a surface pad can be accomplishedby solder reflow methods, heating, laser soldering, welding or the like.

The stripped end of a scribed wire conductor can be inserted into acircuit hole and electrically and mechanical terminated by soldering,heating with a laser or the like.

Termination may also be accomplished by mechanically drilling throughwires to form holes in the substrates and then metallizing, or plating,the drilled hole.

Leaded components may be inserted into circuit holes on the substrateafter the wire conductors have been inserted in the holes and prior totermination. The components may be inserted either manually orautomatically. Both a component lead and wire conductor end may residein the same circuit hole. Once the components are placed, the circuitholes are manually or automatically filled with solder. Circuit holesmay be filled with solder using a wave soldering machine. Thisautomatically produces solder joints between the wire conductor andcomponent leads, or, where circuit holes are metallized, between thewire conductor, wall metallization and the component lead.

The adhesive coated conductor may be stripped before placement on asurface or stripped just prior to termination. Preferably the wire isstripped and cut by an appropriate apparatus just prior to termination.Thus, a conductor may be scribed and stripped along a length sufficientto provide metallized wire for two endpoints: one to end a scribedlength of conductor and another to begin a new length of conductor. Theconductor is cut at a middle point along the stripped section for thispurpose.

The process of this invention may also be used to modify or make acircuit board provided with "parallel holes." These circuit boardspossess a set of plated through holes which are electrically connectedto a corresponding first set of plated through holes. When constructingor repairing boards having parallel holes, the stripped ends of theconductor should be inserted into the duplicate holes and soldered.

Circuit Board Modification

FIG. 1a shows an interconnection circuit board 110a having etched powerand ground planes 111a and 13a on which conductors 116a have beenplaced. A dielectric layer with surface 115a has been applied over theconductors. Circuit holes 120a have been drilled and the hole wallsmetallized in order to provide electrical access between the conductors116a and the conductors on the opposite surface as well as the outsideworld. If it is desired to modify the circuit board depicted in FIG. 1a,such modification can be accomplished according to the process of thisinvention as described below.

FIG. 1b shows the interconnection circuit board 110a of FIG. 1a asmodified in accordance with the process of this invention. Conductor130b having adhesive coating 140b is applied, for example, to surface115b along the predetermined route from circuit hole 126b to circuit128b. The adhesive coating 140b is removed by stripping, e.g. with alaser, from conductor 130b prior to the conductor's insertion intocircuit hole 126b. at segment 132b. Segment 132b is inserted intocircuit hole 126b and the adhesive coating 140b activated, e.g. with arepeated laser beam pulse. The conductor 130b is then scribed ontosurface 115b. The now tacky, activated adhesive coating, providescontinuous adhesion as it is scribed and contacts surface 115b betweenthe conductor 130b and the surface 115b. Conductor 130b is scribed in apredetermined pattern until it reaches circuit hole 128b. At platedthrough hole 128b, adhesive coating 140b is again stripped fromconductor 130b, leaving the conductor exposed at segment 134b. Segment134b is inserted into plated through hole 128b.

The connection between circuit holes 122b and 124b has been severed bydrilling a hole 150b into the board. An additional conductive path issimilarly provided by applying adhesive coated conductor 135b in adefined, predetermined and repeatable location reaching from terminalpoint 122b to terminal point 129b. Both terminal points are metallizedcircuit holes. Connection to hole walls is made by known technologiesand preferably by soldering, welding or the like.

FIG. 1c depicts modified interconnection circuit board 110c aftermodification conductor 130c has been placed as shown in FIG. 1b. Oncethe modifications are made, components 160c may be placed in the circuitholes of the interconnection circuit board in the appropriate locations.A component lead 165c can occupy the same circuit hole barrel asconductor 130c. Once the conductors and the components are in place,electrical and mechanical termination can be made by soldering, forexample.

FIG. 1d depicts the interconnection circuit board after electrical andmechanical interconnection has been made by soldering. The componentleads 165d and conductors 130d have been soldered into circuit holes120d, leaving a fillet of solder 170d. Solder fillet 170d provideselectrical and mechanical interconnection.

FIG. 1e depicts a multiple layer interconnection circuit board 180ehaving an etched power layer 182e, an etched ground layer 184e and anetched signal layer 116e. Modification conductors 130 have been scribedto the surface of board 180e to provide a new signal interconnectionpattern.

FIG. 2a shows an interconnection circuit board 200a having surface pads240a. A short conductor 231a is located on surface 215a andinterconnects surface pads 241a and 242a.

FIG. 2b shows the interconnection circuit board 200a of FIG. 2a asmodified in accordance with the process of this invention to addconductors 232b and 234b. A conductor, for example conductor 232b, isfirst stripped of the adhesive coating and insulation layers at one endand attached to a surface pad 240b by soldering, welding or the like.This attachment provides electrical and mechanical interconnection atthe surface pad terminal point. Conductor 232b is then scribed andbonded by the activated adhesive coating 233b along its path. The otherend of conductor 232b is then stripped, and attached to surface pad243b. Conductor 234b is similarly scribed, bonded, and stripped tointerconnect the appropriate surface pads. Once the conductorinterconnection pattern is formed, the surface-attached components canbe placed and attached to the surface pads.

FIG. 2c depicts the completed interconnection board of FIGS. 2a and 2bwith surface component 210c attached.

FIG. 3a depicts modification of an interconnection circuit board onwhich there is located a surface-attached component 312 and adual-in-line package 310. Duplicate parallel repair holes 320a wereprovided in the board design to allow access to terminal points aftercomponent insertion. This type of interconnection circuit board can bemodified even after components have been attached or inserted. Themethod for modifying this type of interconnection circuit board is shownin FIGS. 1a-1d.

Conductor 330a having adhesive coating 340a is stripped at one end. Thestripped portion is inserted into circuit hole 335a. Conductor 330a isthen routed and affixed to surface 315a. When conductor 330a reachesterminal point 336a, it is again stripped and inserted into the circuithole barrel 338a. Electrical termination can be made as the conductorsare inserted into the plated through holes at the terminal points bysoldering or the like. However, electrical connection can be made afterall the modification conductors have been scribed to the board.

FIG. 3b depicts another modification technique for an interconnectioncircuit board on which there are located surface-attached components andlead inserted components. Duplicate parallel repair surface pads 335bare provided in the board design to allow access to terminal pointsafter component insertion and attachment. This type of interconnectioncircuit board can be modified using the technique previously describedand depicted in FIG. 2.

Conductor 330b having adhesive coating 340b and an insulation layer isstripped at one end. The stripped portion is affixed to a surface pad335b. Conductor 330b is then routed and affixed to surface 315b byactivated adhesive coating 340b. When conductor 330b reaches terminalpoint 336b, it is stripped at the other end and affixed to surface pad338b at that terminal point. Electrical termination can be made as theconductors are affixed to the surface pads at the terminal points bysoldering or the like.

FIG. 4a depicts a standardized prefabricated panel of pads and holessuitable for various component sizes and component pin densities. Thecomponents which are to be used in the circuit are first matched to theexisting pads and holes on the circuit board panel. The locations andsizes of the circuit board holes are standardized to accommodate avariety of different circuit configurations utilizing the same basiccircuit board panel. The basic panel 410 contains power and groundplanes 420a and 430a. Circuit holes 450a are drilled and metallizedprior to scribing conductors. Surrounding the holes are conductive pads470a for eventual termination of conductors. FIG. 4b depicts basicstandardized panel 410 of FIG. 4a with adhesive coated conductors 482band 484b providing an electrical interconnect. Adhesive coating 486bbonds conductors 482b and 484b to surface 400b. FIG. 4b furtherillustrates how the adhesive coating 486b provides adequate bonding atcrossover 480b of conductors. Adhesive coating 486b appears betweenconductor 482b and 484b at crossover 480b.

Conductor 482b having adhesive coating 486b is stripped at one end andthe stripped portion is affixed to surface pad 472b. Conductor 482b isthen routed and affixed to surface 400b. When conductor 482b reachesterminal point 422b, it is again stripped and affixed to surface pad474b by soldering at that terminal point. Electrical connection can bemade as the conductors are affixed to the surface pads at the terminalpoints by soldering or the like.

FIG. 4c shows the completed circuit board 410c with lead insertedcomponent 465c mounted on the board. The leads 460c of the component aresubsequently mechanically and electrically connected to the circuitboard 410c by soldering or the like.

FIGS. 5a to 5c illustrate construction of a new circuit board using theprocess of this invention. FIG. 5b shows the starting circuit boardpanel with etched power and ground planes 520a and 530a. Circuit holes540a and 542a are drilled. The holes are then metallized, and surfacepads 544a and 546a formed around holes 540a and 542a. Surface pads 548aand 549a are placed on the surface 500a for surface attached components.

FIG. 5b depicts the prefabricated panel 510b as it appears afteradhesive coated conductors 582b, 584b, and 592b have been scribed to itssurface. The adhesive coating is activated as the conductor is beingscribed and serves to bond conductors 582b, 584b and 592b to surface500b. Adhesive coating 586b also provides adequate bonding at thecrossover 580b of conductors 582b and 584b.

Sequentially, conductor 582b can be first stripped at one end and thestripped portion attached to surface pad 572b by soldering. Conductor582b is then scribed to surface 500b. When conductor 582b reachesterminal point 522b, its endpoint is stripped and soldered to surfacepad 574b at that terminal point. Conductor 592b is stripped and solderedto surface pad 544b. This conductor is then routed and soldered tosurface 500b and when it reaches terminal point 524b, the other end isstripped and conductor 592b is soldered to surface pad 546b. Electricalconnection is made when the conductors are affixed to the surface padsat the terminal points by soldering or the like. Conductor 584b issimilarly stripped, scribed and connected. The completed circuit boardwith components mounted thereon appears as shown in FIG. 5c.

FIG. 6 illustrates another embodiment of the invention wherein adhesivecoated conductors are applied to both sides of the circuit board andthereafter encapsulated.

The initial circuit board 610 is constructed including interior groundand power planes 612 and 614 as well as printed surface conductors 618and 620 which can provide terminal pads and, if desired, a conductorinterconnection pattern. Adhesive coated conductors 622 are then addedto the upper surface of the board with stripped ends connected toterminal pads like terminal pad 620. Similarly adhesive coatedconductors 624 are added to the lower surface with stripped endsconnected to terminal pads like terminal pad 618. Thereafter the surfaceconductors are encapsulated by encapsulating layers 626 and 628. Theencapsulated board is then drilled and the drilled holes metalized toprovide terminal holes 630 connected to the interior conductors andlayers. Components 632 can thereafter be mounted with leads 634 insertedinto the terminal holes and connected by solder (not shown).

What is claimed is:
 1. A process for scribing at least one conductoronto a surface of a substrate in a predetermined pattern between twopoints spaced apart on the surface each defining a terminal pointcomprising:a. providing a conductor having an adhesive coating, which isnormally non-tacky and non-blocking prior to curing, which can beactivated by applying energy thereto, said adhesive coating rapidlyreverting to a solid non-tacky condition within about 0 to about 200miliseconds after activation; b. scribing the conductor onto the surfaceof the substrate from a first terminal point along a predetermined pathto a second terminal point; c. activating at least a portion of theadhesive coating on the conductor prior to, or simultaneously withcontact with the substrate surface so that a bond is formed adhering theconductor to the surface of the substrate when said activated adhesivereverts to said solid non-tacky condition; said reversion of saidadhesive to a non-tacky state within about 0 to 200 millisecondspermitting the scribing speed along a straight path to reach a potentialspeed of at least 120 inches per minute while simultaneouslysubstantially avoiding relative movement of the bonded conductors withrespect to each other and the substrate surface.
 2. A process accordingto claim 1 wherein said adhesive coating rapidly reverts to a solid,non-tacky condition after activation.
 3. A process according to claim 2further including the step of cutting the conductor after scribing theactivated portion of the conductor such that the cut end of theconductor lies substantially at the second terminal point.
 4. A processaccording to claim 1 further including the step of stripping theconductor to expose its conductive portion prior to scribing theconductor.
 5. A process according to claim 1 further including the stepof stripping the conductor to expose its conductive portion subsequentto scribing the conductor.
 6. The process of claim 1 wherein theconductor provided has an adhesive coating comprising three componentsasa first component a film forming polymeric resin having an averagemolecular weight between about 10,000 and about 100,000 and having anepoxide, hydroxyl or unsaturated functionality greater than 2, saidpolymeric resin being selected from the group consisting of polyesters,polyurethanes, polyethers, epoxies, allyl polymers and acrylics; as asecond component a filler, or a polyfunctional compound, or mixturesthereof, said polyfunctional compounds having an average molecularweight below 7,000 and containing a polyphenol backbone, and as a thirdcomponent a curing agent capable of reacting or initiating a reactionwith the functional groups of the polymeric resin to form crosslinks andcure the polymeric resing to a C-stage.
 7. A process for making aninterconnection circuit board on an insulating base substrate having aplurality of points spaced apart on the surface of the substrate eachdefining a terminal point comprising:a. providing at least one conductorhaving an adhesive coating, the adhesive coating being non-tacky,non-blocking and flexible prior to curing and which can be activated byheat, radiant or ultrasonic energy or by a combination thereof saidadhesive coating rapidly reverting to a solid non-tacky condition withinabout 0 to about 200 milliseconds after activation; b. activating aportion of the conductor having activated adhesive coating the conductorprior to or simultaneously with scribing the activated portion of thesurface; c. scribing the activated portion of the conductor onto thesurface from a first terminal point along a predetermined, precise andreproducible pattern to a second terminal point, thereby adhering theconductor to the surface by means of the adhesive coating; said rapidreversion of the coating permitting the scribing speed along a straightpath to reach a potential speed of at least 120 inches per minutes,simultaneously allowing the conductor pattern to retain dimensionalstability.
 8. The process of claim 7 wherein the adhesive coating on theconductor comprises three components:as a first component a film formingpolymeric resin having an average molecular weight between about 10,000and about 100,000 and having an epoxide, hydroxyl or unsaturatedfunctionality greater than 2, said polymeric resin being selected fromthe group consisting of polyesters, polyurethanes, polyethers, epoxides,allyl polymers and acrylics; as a second component a filler, or apolyfunctional compound, or mixtures thereof, said polyfunctionalcompounds having an average molecular weight below 7,000 and containinga polyphenol backbone, and as a third component a curing agent capableof reacting or initiating a reaction with the functional groups of thepolymeric resin to form crosslinks and cure the polymeric resin to aC-stage.
 9. A process for modifying an interconnection circuit board byscribing at least one conductor onto a surface of the interconnectioncircuit board in a predetermined pattern beween two points spaced aparton the surface each defining a terminal point comprising:a. providing anelongated performed conductor having an adhesive coating, the adhesivecoating being non-tacky, non-blocking and flexible prior to curing andwhich can be activated by thermal, radiant or ultrasonic energy or acombination thereof, said adhesive coating rapidly reverting to a solidnon-tacky condition within about 0 to about 200 milliseconds afteractivation; b. activating a portion of the conductor having activatedadhesive coating prior to or simultaneously with scribing the activatedportion of the surface; c. scribing the activated portion of theconductor onto the surface from a first terminal point along apredetermined, precise and reproducible pattern to a second terminalpoint, thereby adhering the conductor to the surface by means of theadhesive coating; said rapid reversion of the coating permitting thescribing speed along a straight path to reach a potential speed of atleast 120 inches per minute, simultaneously allowing the conductorpattern to retain dimensional stability.
 10. The process of claim 9wherein the adhesive coating on the conductor comprises threecomponents:as a first component a film forming polymeric resin having anaverage molecular weight between about 10,000 and about 100,000 andhaving an epoxide, hydroxyl or unsaturated functionality greater than 2,said polymeric resin being selected from the group consisting ofpolyesters, polyurethanes, polyethers, epoxies, allyl polymers andacrylics; as a second component a filler, or a polyfunctional compound,or mixtures thereof, said polyfunctional compounds having an averagemolecular weight below 7,000 and containing a polyphenol backbone, andas a third component a curing agent capable of reacting or initiating areaction with the functional groups of the polymeric resin to formcrosslinks and cure the polymeric resin to a C-stage.
 11. A processaccording to claim 1, 7 or 9 wherein said energy for activating theadhesive coating is applied by means of a pulsed laser beam wherein thepulses emitted from said laser beam are constant in energy, and thepulse repetition rate is a function of the length of the conductorscribed independent of the scribing speed.
 12. A process according toclaim 11 wherein said energy for activating the adhesive coating isapplied by means of laser energy, hot air or ultraviolet or acombination thereof and wherein said energy means is directed at theprojected point of contact between the conductor and the surface of thesubstrate.
 13. A process according to claim 9 wherein the conductorpattern formed by the scribed conductors can be reproduced on aplurality of boards such that the patterns formed have reproducibleelectrical characteristics.
 14. A process according to claim 1, 7 or 9wherein said adhesive coating is capable of adhering to a plurality ofsurfaces with different finishes or properties comprising the surface ofthe substrate to be modified.
 15. A process according to claim 1, 7 or 9where in said adhesive coating is capable of adhering, when activated,to one or more solid surface materials selected from the groupconsisting of polymer resins, ceramics, glass-bonded metal or carbonconductors, polymer-bonded metal or carbon powder conductors, andconductive polymer materials.
 16. A process according to claim 1, 7 or 9wherein said thermal energy for activating the adhesive coating isapplied by means of heated fluid or a solid heat applicator.
 17. Aprocess according to claim 1, 7 or 8 wherein said adhesive is athermosetting resin capable of being C-staged by application of heat orlight.
 18. A process according to claim 1, 7 or 8 wherein said adhesiveis a thermoplastic resin.
 19. A process according to claim 1, 7 or 8wherein said adhesive coating is no activated at a conductor endpoint.20. A process for scribing at least one conductor onto a surface of asubstrate in a predetermined pattern between two point spaced apart onthe surface each defining a terminal point, said process comprising:a.providing a conductor having an adhesive coating, which is normallynon-tacky and non-blocking prior to curing, which can be activated byapplying laser energy thereto, and which reverts to a solid non-tackycondition after activation; b. scribing the conductor onto the surfaceof the substrate from a first terminal point along a predetermined patha second terminal point; c. activating at least a portion of theadhesive coating on the conductor prior to, or simultaneously withcontact with the substrate surface by means of predetermined energylevel laser pulses having a constant energy level selected to activateadhesive within the laser beam so that a bond is formed adhering theconductor to the surface of the substrate when said adhesive soactivated reverts to said solid non-tacky condition, the pulserepetition rate being adjusted as a function of scribing speed todeliver a fixed number of constant energy pulses per unit length ofconductor.
 21. A process according to claim 20 wherein the area alongthe conductor irradiated by each successive pulse overlaps the areairradiated by the preceding pulse.
 22. A process according to claim 20wherein the pulse width of said laser pulses is from about 200 to about2000 microseconds, the pulse amplitude is about 20 watts, the length ofthe area of adhesive coating irradiated by the pulse is from about 0.5to about 2.5 mm, the laser beam is pulsed each time a length ofconductor from about 0.1 to about 0.25 mm is scribed.
 23. A process forscribing a conductor to the surface of a substrate wherein saidconductor has an adhesive coating which is non-tacky, non-blocking andflexible and which can be activated by means of a laser beam which isdelivered in substantially uniform discrete quanta of energy with thepulse repetition rate being a function of the length of conductorscribed, or the scribing speed, or a combination thereof, activating aportion of the adhesive coating and scribing the activated portion ofthe conductor to the surface.
 24. A process according to claim 23wherein said means for activating the adhesive coating is ultrasonicenergy.
 25. A process for scribing a conductor to the surface of asubstrate wherein said conductor has an adhesive coating which isnon-tacky, non-blocking and flexible and which can be activated by meansof a pulsed laser beam which is delivered in substantially uniformdiscrete quanta of energy with the pulse repetition rate bein a functionof the length of conductor scribed, or the scribing speed, or acombination thereof, activating a portion of the adhesive coating andscribing the activated portion of the conductor to the surface, saidadhesive coating containing regions of microencapsulated adhesivematerial capable of being released by pressure, said process comprisingthe further step of applying sufficient pressure to said adhesivecoating to release the adhesive material at or close to the point ofcontact with the substrate surface such that the adhesive material formsa bond between the conductor and the substrate.
 26. A process forscribing at least one insulated conductor onto a surface of a substratein a predetermined pattern between two points spaced apart on thesurface each defining a terminal point comprising:providing a conductorhaving an adhesive coating,which is normally non-tacky and non-blockingprior to activation or curing, which can be activated by applying energythereto, and which reverts to a solid non-tacky condition afteractivation; stripping the adhesive coating and insulation from theconductor at one end; scribing the conductor onto the surface of thesubstrate from said end of the conductor at a first terminal point alonga predetermined path to a second terminal point; activating at least aportion of the adhesive coating on the conductor prior to, orsimultaneously with contact with the substrate surface so that a bond isformed adhering the conductor to the surface of the substrate when saidactivated adhesive reverts to said solid non-tacky condition; cuttingthe conductor in the vicinity of the second terminal point; andstripping the adhesive coating and insulating layer in the vicinity ofthe cut end.
 27. A process according to claim 26 wherein said insulatinglayer and adhesive coating is removed by a stripping means selected fromthe group consisting of a chemical means, a mechanical means and aradiant energy means.
 28. A process according to claim 26 wherein theconductive portion of the conductor is a metallic wire, the terminalpoint is a plated through hole in the substrate and further includingthe step of inserting the exposed portion of the conductor into theplated through hole and filling the hole with solder.
 29. A processaccording to claim 28 further including the step of inserting acomponent lead or other electrical contact into the hole prior to saidsoldering step.
 30. A process according to claim 26 wherein theconductive portion of the conductor is a metallic wire, the terminalpoints are a plated through holes, further including the steps ofinserting the exposed portion of the conductor into a first hole;scribing said conductor along a predetermined path to the vicinity of asecond hole; removing the insulating layer and adhesive coating from alenqth of the conductor; cutting the conductor and inserting it into thesecond hole.
 31. A process according to claim 26 wherein the conductiveportion of the conductor is a metallic wire and the terminal points aresurface pads, further including the steps of soldering the exposedportion of the conductor to a first surface pad; scribing said conductoralong a predetermined path to the vicinity of a second surface pad;removing the insulating layer and adhesive coating from a length of theconductor; cutting the conductor and soldering it to the second surfacepad.
 32. The process according to claim 26 wherein the adhesive coatingon the conductor comprises three components:as a first component a filmforming polymeric resin having an average molecular weight between about10,000 and about 100,000 and having an epoxide, hydroxyl or unsaturatedfunctinality greater than 2, said polymeric resin being selected fromthe group consisting of polyesters, polyurethanes, polyethers, epoxies,allyl polymers and acrylics; as a second component a filler, or apolyfunctional compound, or mixtures thereof, said polyfunctionalcompounds having an average molecular weight below 7,000 and contining apolyphenol backbone, and as a third component a curing agent capable ofreacting or initiating a reaction with the functional groups of thepolymeric resin to form crosslinks and cure the polymeric resin to aC-stage.
 33. A process for scribing at least one insulated conductoronto a surface of a substrate in predetermined pattern between twopoints spaced apart on the surface each defining a terminal pointcomprising:providing a conductor having an adhesive coating, which isnormally non-tacky and non-blocking prior to activation or curing, whichcan be activated by applying energy thereto, and which reverts to asolid non-tacky condition after activation; stripping the adhesivecoating and insulation from the conductor at one end; scribing theconductor onto the surface of the substrate from said end of theconductor at a first terminal point along a predetermined path to asecond terminal point; activating at least a portion of the adhesivecoating on the conductor prior to, or simultaneously with contact withthe substrate surface so that bond is formed adhering the conductor tothe surface of the substrate when said activated adhesive reverts tosaid solid non-tacky condition; cutting the conductor in the vicinity ofthe second terminal point; and stripping the adhesive coating andinsulating layer in the vicinity of the cut end by a stripping means,said stripping means is a radiant energy means comprising a CO2 laserbeam having a spot size sufficient for evaporating the adhesive coatingand the insulating layer which is scanned repeatedly along apredetermined length of conductor.
 34. A process according to claim 33wherein said stripping means is an Excimer laser beam whichphotodecomposes the insulating layer and adhesive coating.